265/70R18 vs 285/70R17
Switching from 265/70R18 to 285/70R17 increases the overall diameter by 2.6 mm (0.3%). That is within the usual ±3% guideline.
| 265/70R18 | 285/70R17 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 265 mm | 285 mm | +20.0 |
| Sidewall height | 185.5 mm | 199.5 mm | +14.0 |
| Rim diameter | 457.2 mm | 431.8 mm | -25.4 |
| Overall diameter | 828.2 mm | 830.8 mm | +2.6 |
| Circumference | 2,601.9 mm | 2,610.0 mm | +8.1 |
| Revolutions | 384 per km | 383 per km | -1.0 |
Speedometer effect
With 285/70R17 fitted on a car calibrated for 265/70R18, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.2 km/h |
| 80 km/h | 80.3 km/h |
| 100 km/h | 100.3 km/h |
| 120 km/h | 120.4 km/h |
Larger tires make the car go faster than the speedometer shows. Most speedometers also read slightly high from the factory.
Before you change size
- Check the sizes approved for your vehicle on the door-jamb placard or in the owner's manual.
- Check clearance to suspension, brakes and arches at full lock and full compression.
- Match or exceed the original load index and speed rating.
- Wider tires need an appropriate rim width; a 285 mm tire has a manufacturer-specified rim width range.
265/70R18 dimensions · 285/70R17 dimensions · Open in calculator